1. Field of the Invention
Embodiments disclosed herein relate generally to kill fluids used in the completion of oil and gas wells.
2. Background Art
Kill fluids are commonly placed in a wellbore during oil field wellbore operations, such as wellbore completions, to kill the well, i.e., prevent the influx of formation fluids into the wellbore and the loss of wellbore fluids to the formation while the well is open. The kill fluid is often maintained in the wellbore for the entire duration of the operation.
Conventional kill fluids known in the art are typically aqueous liquids, which contain a weighting agent, such as inert inorganic solids in solution or suspension, to increase the density of the fluid. The weighted kill fluid applies a hydrostatic pressure against the formation fluid, which is greater than the pressure exerted by the formation fluid attempting to intrude into the wellbore. This overbalanced hydrostatic pressure prevents the ingress of formation fluids into the wellbore during performance of the given oil field wellbore operation, which is necessary from an operational standpoint to prevent interference from formation fluids, as well as from a safety standpoint to prevent blowouts and well kicks.
Thickeners are often included in weighted kill fluids to provide for leakoff inhibition. Fluid leakoff can undesirably result in formation damage, i.e., permeability reduction, resulting in reduced hydrocarbon recovery or reduced injectivity into the formation.
In particular, advantageous kill fluids are those that not only prevent formation fluid influx into the wellbore, but also prevent appreciable wellbore fluid leakoff into the formation. Kill fluids achieve their fluid loss control from the presence of specific solids that rely on filtercake build up on the face of the formation to inhibit flow into and through the formation. However, these additive materials can cause severe damage to near-wellbore areas of the formation after their application. This damage can significantly reduce production levels if the formation permeability is not restored to its original level. Further, at a suitable point in the completion operation, the filter cake must be removed to restore the formation's permeability, preferably to its original level.
After any completion operations have been accomplished, removal of filter cake formed from the kill fluid remaining on the sidewalls of the wellbore may be necessary. Although a kill fluid may be essential to completion operations, the barriers can be a significant impediment to the production of hydrocarbon or other fluids from the well if, for example, the rock formation is still plugged by the barrier. Because filter cake is compact, it often adheres strongly to the formation and may not be readily or completely flushed out of the formation by fluid action alone.
Accordingly, there exists a need for a kill fluid that may effectively reduce the ingress and egress of fluids between the formation and wellbore during a completion operation but also minimizes formation damage.